BIOGEOCHEMICAL CYCLING OF BIOGENIC CARBON IN OCEANS: AN ALTERNATIVE ROLE FOR THE MICROBIAL FOOD WEB

The processes that occur within the microbial food web and the coupling between microbes and metazoans influence the remineralization of biogenic carbon (BC) in the surface layer, the partitioning of BC between dissolved and particulate pools and, consequently, BC export to depth and to large animals. Both dissolved (DOC) and particulate organic carbon may be exported in proportions that vary with local and mesoscale conditions. Numerous studies have investigated the potential role of the microbial food web in channelling BC from DOC to metazoa, but the actual role of microbes in controlling the BC fluxes may differ from that previously proposed.Heterotrophic microbes dominate respiration in the ocean, and the remineralization of BC to CO2 impedes the export of organic carbon. When inorganic nutrients or temperature limit bacterial growth or when grazers constrain bacterial stocks, less DOC is taken up by bacteria. It follows that, when the activity of the microbial food web is low, more DOC and hence, BC is available for export to depth and potential sequestration.